Extract from ABC News
Tonight's full moon will be a rare occurrence, but won't look all that different. (Supplied: NASA/GSFC/Arizona State University)
Tonight's full moon will mark a rare occasion.
It will be both a micromoon as well as a blue moon.
But don't expect to see drastic changes when you look up at the sky this evening.
What is a micromoon?
If you've ever heard of a supermoon, think of a micromoon as its opposite.
A micromoon is a term used to describe when a full moon occurs at the same time as the Moon being at its apogee.
That means it's pretty much at its furthest point from Earth in its oval-shaped orbit.
This graphic from NASA gives you a good idea of how it works:
The Moon orbits on more of an oval-shaped path than a perfect circle. (YouTube: NASAJPL Edu)
The Moon itself doesn't change; a micromoon will just look slightly smaller than a regular full moon looks.
A supermoon looks slightly bigger.
It'll be difficult to see the difference in apparent size when you look up at the Moon tonight, but it's noticeable in comparison images such as the one posted on NASA's popular Astronomy Picture of the Day blog over the weekend.
The image is made up two different photos taken by Soumyadeep Mukherjee months apart.
On the left is a supermoon taken in December 2021, while the right is a micromoon in May, 2021.
Soumyadeep Mukherjee's photos of the Moon were taken months apart in 2021. (Supplied: Soumyadeep Mukherjee)
Mr Mukherjee said he used the "same camera, same lens and same focal length in order to keep the image scale the same".
"This ensured that the size comparison between the two moons are kept the same."
He took both photos in Kolkata, eastern India, where May can mean cloudy weather, which can complicate lunar photography.
"I was rather nervous in the month of May, which is just before the monsoon arrives," Mr Mukherjee said.
"But luckily, I was able to capture both the moons with clear skies."
'Smallest' micromoon of the year
Part of the reason tonight's full moon is generating so much social media buzz is because it'll be the smallest micromoon of the year.
"Just after sunset, a full moon will appear slightly smaller and dimmer than usual," the editors of the Astronomy Picture of of the Day blog wrote.
"In fact, tonight's micromoon will be the farthest, smallest, and dimmest moon this year."
This month's full moon will occur when the Moon is 406,368 kilometres from Earth, David Dickenson explained for The Universe Today.
Rare pairing with a blue moon
Tonight's micromoon will also be what's called a blue moon.
In this context, a blue moon refers a second full moon in a calendar month.
NASA says blue moons usually only happen every two to three years.
But for a blue moon to occur at the same time as a micromoon is pretty rare.
"Although the next micromoon occurs next month, and the next blue moon at the end of 2028, the next blue micromoon will not occur until 2053," the Astronomy Picture of the Day blog says.
The last micromoon and blue moon was in October 2020, Mr Dickenson said.
He called tonight's full moon a "last in a generation" occurrence.
It's rare for a blue moon to coincide with a micromoon. (Supplied: @luke_van_de_rest)
Will the Moon look blue?
No.
The "blue" part in the phrase "blue moon" has nothing to do with the colouring of the Moon.
It's believed to have come from an article in an astronomy magazine in the 1940s.
"This colourful term is actually a calendrical goof that worked its way into the pages of Sky & Telescope back in March 1946, and it spread to the world from there," Kelly Beatty wrote in an article published on the magazine's website in 2009.
Sky & Telescope explained that its writer James Hugh Pruett "made an incorrect assumption about how the term had been used in the Maine Farmers' Almanac".
The Old Farmer's Almanac is an American annual magazine that contains things like weather pattern forecasts, moon phases and gardening tips.
But the Moon has appeared to be blue in colour before, with NASA pointing to a famous example from 1883.
"People saw blue moons almost every night after the Indonesian volcano Krakatoa exploded with the force of a 100-megaton nuclear bomb," NASA's science editorial team wrote.
"Some of the plumes were filled with particles 1 micron wide, about the same as the wavelength of red light.
"Particles of this special size strongly scatter red light, while allowing blue light to pass through.
"Krakatoa's clouds thus acted like a blue filter."
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